Method of purifying a phenol by distillation



. mium or in one having a chromium lining water-white pure product.

Patented Sept. 29, 1931 UNITED STATES PATENT OFFICE EDGAR C, BRI'I'TON, OF MIDLAND, MICHIGAN, ASSIGNOR TO THE DOW CHEMICAL COM- PANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN METHOD OF PUBIFYING A PHENOL BY DISTILLATION No Drawing.

The present invention concerns an improvement in methods of distillation of phenol for the production of a persistently It has been customary practice to distill phenol through a fractionation column to a condenser, discarding the first distillate containing the water and-retaining the subseuent distillate as product. There is left in tie still the tarry residue. Various procedures have been adopted in the effort to secure a satisfactory water-white pure product, the condensation of the final product being conducted in apparatus constructed either of iron, tin or silver, for example. The product obtained by such methods is, however, not fully satisfactory inasmuch as it contains such metals as iron, tin or silver in easily detectible amounts and there is suffered in addition a gradual deterioration of the condenser which must be eventually replaced, addin to the cost of treatment.

If a liter of t e product obtained by such distillation be concentrated, the residue will show by chemical tests the presence of the metal of which the condenser is made, such namely as iron, tin or silver, in substantial amounts.

I have found that a product markedly superior to that obtainable b the above customary method may be ha by condensing the product in a metal condenser of chrosuch as may be secured by plating the metal condenser surface with chromium.

To the accomplishment of the foregoing and related ends the invention then consists of the'features hereinafter fully described Application filed September 15, 1928. Serial No. 306,293.

tionation column and for continuously withdrawing the excess thereof as product. The fractionation column may, however, be connected with a reflux condenser in which a portion only of the vapor is condensed and returned to the column followed by a. final condenser for the condensation of the vapor leaving the reflux condenser. In both such cases the equipment will be preferably operated under vacuum by connecting the vapor outlet from the reflux condenser in the first instance, or a similar outlet from the final condenser in the second instance, to a suitable source of vacuum whereby the distillation may be carried out under reduced pressure. By placing the condensers at a suitable elevation the product may be drawn off as produced through a vacuum leg or sealed hydrostatic column.

The first fraction coming over containing the water will be discarded and the suc ceeding fraction, water-free, will constitute, as in current practice, the final product.

The above described arrangements are in common use and known to those versed in the art of distillation.

In current practice the combined reflux and final condenser in the first instance would be fitted with iron, tin or silver condensing surfaces and preferably with a vapor pipe of the same material between the fractionation column and the condenser. In the second instance the refluxcondenser may be of any suitable metal and only the vapor pipe from it to the final condenser and the condensing surface in said final condenser would be made of iron, tin or ,silver, since this is the only surface on which the final product is condensed.

I may use in the practice of my invention either of the arrangements heretofore described or others in which the surfaces,

' chromium.

the condenser shall not carry entrainment condensed upon a contaminating surface. A suitable entrainment separator of the bafile or other type may advantageously precede the vapor pipe, preferably at the point where it leaves the fractionation column, or such entrainment separator may be included in the upper portion of the column structure. Such a separator or entrainment catcher is intended to prevent contaminated liquid particles passing from the column into the vapor pipe through which they might be carried forward into the condenser.

The precise construction of the condenser is immaterial to the practice of my invention, customary or special forms being permissible so long as the surfaces with which the final product contacts are of chromium metal.

I have compared phenol condensed in iron, tin and silver condensers with phenol condensed in a chromium lined condenser. The latter shows a content of iron very much less than 0.1 part-per million and chromium was not detected by chemical tests. A hi her test for the presence of metals was tound in the product customarily obtained. The entire absence of chromium from the phenol condensed on a surface thereof indicates a very desirable long life, if not complete permanence, of the condensing surface.

I have also subjected phenol from metal condensers to prolonged sunlight tests and find the product condensed on chromium to be not only water'white but to exhibit a marked superiority in permanence of clearness and water-whitnes's over that condensed on iron, silver or tin.

My invention accordingly represents a distinct and valuable advance in the art of distilling phenol for the production of a pure product since there is obtained thereby a product having markedly superior qualities of initial and permanent water-whiteness in comparison with the customary product. Such product shows a lower .test for metals and the entire absence of chromium indicates a highly desirable immunity from attack and permanence of the condenser.

My herein disclosed invention is further applicable to the condensation of vapors of phenol, whether derived by distillation of natural or synthetic phenol, and is further being made as regards the details disclosed provided the steps stated in any one of the following claims or the equivalent of such be employed.

I therefore particularly point out and distinctly claim as my invention 1. The method of producing a persistent- 1y water white phenol by condensing the tilling such phenol and condensing the vapors thereof in contact with condenser surfaces consisting of metallic chromium.

Signed by me this llth'day of September EDGAR C. BRITTON.

applicable to the condensation of vapors J containing phenol where such phenol would be disadvantageously contaminated if condensed upon metal surface other than My herein disclosed invention is further applicable in general to the distillation of phenols, e. g., cresols, xylenols, naphthols, hydroxydyphenyl, etc.

Other modes of applying the principle of my invention may be employed, change 

